DIY Installation in Derry

[cye]

Here's George Row's great description of his and Mary Kay Mullan's DIY solar water heating panel installation...

veryireland.com/energy/Installing-Solar-Water-Heating/

George and Mary Kay have 20X58mm evacuated tubes plumbed indirectly into their pre-existing 120L tank using a retrofit immersion coil. Pump is a 12v dc low power pump.

[grow]

Cye,
We had an odd problem on Saturday.

I noticed that the pump had stopped and on checking found that the temperature at the panel was over 150°C. So the pump had cut out ... I put the pump on in manual mode and the temperature came down a BIT but was still over 100°C

So I repeatedly put the pump on manual and waited for the sun to go down.

My guess is that some air had got into the circuit - after some water had got out obviously.

When the temperature got down to about 80°C I went up to the attic and - with the pump on and the water-main top-up on - I opened the bleeder valves at the panel level ... but despite waiting for a couple of minutes it never got to the point where the water had reached the bleeder.

So I am guessing that we are going to have to drain the whole system down and start again.

Any thoughts that you have about what might be going on or how to fix a system that has spent a day boiling itself would be very welcome.

George

PS I posted this as a reply to this message because I couldn't find a way to start a new thread.

[caveman]

George,
I had a similar problem with my system. When my pump stopped (power failure) the water in panel boiled and was lost as steam through the auto air vent.
However when I recharged the system everything was ok.
What caused the pump to stop? and where did the water go as you tried to top up? What pump station do you have?
Conor

[grow]

Conor,
Thanks for that reassurance.

I have this controller:
. www.solarproject.co.uk/controller%20detail.html
controlling this:
. www.youtube.com/watch?v=46U6Owh9pok
pump.

Today I repeatedly - about every half hour or so - opened a bleeder valve, up at the top of the solar circuit, for a few seconds while the pump was on. Most times I would get a "pufft" as a little air came out. It never got to the point where there was coolant/water at that level but I THINK it was shifting some of the air that had been trapped in the system and getting more water into the solar loop.

Gradually as the day went on the panel temperature dropped and it didn't go beyond "normal operating temperatures" at any point today. Having said that today was nothing like as sunny as yesterday.

As for where the water went in the first place ... I don't think there are any major leaks. I suspect that the panel has been having the occasional over-heating episode and steam has been venting - we were away for a week recently when it was sunny here. So it may have initially happened then when there was no one here to use the hot water.

Yesterday was very sunny here. So my current theory is that having overheated while we were away the system went into yesterday with less than a full quota of water and I think it got into a negative-spiral of venting-steam-because-it-was-overheating and then having even less water in the system was overheating all the more ... and venting more etc

The first thing I noticed yesterday was the lack of pump noise ... but it had probably been off for an hour or so before I noticed. I suspect that it had been turned off by the controller due to the panel temperature having gone outside normal operating temperature range. By the time I got into the attic the insulation sleeve nearest the panel had melted which looked sort of scary.

I am going to go on with my repeated bleed/top-up cycles tomorrow morning and if the system gets into behaving normally on a sunny day I will leave it until our plumber is available to drain it down completely and refresh the anti-freeze and fill it properly.

The way our solar loop is filled is a good deal messier than it needs to be. I think that is something that we could have designed better in our system. For example the coolant system in a car-engine manages to have a sealed system that has an expansion/top-up tank. I might talk to the plumber about ways that we could improve it to avoid this happening again.

George

[grow]

Hi Folks,
I got the plumber here this morning. He called here on his way to his "proper job". I think our house is blessed with some sort of favoured-nation status because he regards our solar-hot-water system as more interesting than whatever routine job he was on his way to.

I think we may have found the source of the problem.

When installing the system he had put a mains-pressure-reduction valve on the mains input, so as to be able to control the mains pressure that goes into the solar loop when the top-up valve is opened.

That pressure reduction valve seems to have failed. No matter how it was set it was letting only a tiny dribble through. So we bypassed it just now and were able to top up the solar loop, while bleeding out the air at the top and we did finally (unlike yesterday) get to the point where we got water at the bleeder valve at the top.

So the system is behaving normally for the moment. The plumber has gone to get a replacement for the mains-pressure-reduction valve and I have ordered some high temperature insulation sleeves to replace the ones that melted.

This episode illustrates what must be one of the many corollaries to Murphy's law ("Anything that can go wrong will.") that:
"You will only discover that a remedial system has failed, after the problem that it is intended to remedy, has occurred."
and of course the corollary to this corollary is that:
"When the remedial system fails it will do so in such a way that it turns the minor problem, that it was meant to fix, into a major crisis."

As you can tell from the above my mood has changed and I now no-longer feel the sense of dread that comes to someone who has an inexplicable steaming monster perched on the roof of his house. :-)

George

[caveman]

George,
That's good news. Now you will have so much hot water you will have to invite everyone in the street in to have a bath just to use it all!
Would you mind if we used some of your installation photos for the workshop presentation? Particularly the pics showing the manifold being fitted with tubes?
conor

[grow]

Conor,
Yes - help yourself - that is why they are there.

Drop me an email if you need a higher resolution version of any of them.
[my username here is my email username at Apple's me-dot-com email service - I hope that makes it obvious without publishing it.]

George

[cye]

george

just wondering whether have you a heat dump fitted?

if not, there are some really simple solutions to dumping excess heat.

rgds

cye

[grow]

Cye,

Yes there is a heat-dump on the hot tank - an electrical valve that is triggered by the controller when the top of the tank exceeds a threshold (I think it is set at 80°C), and there is a pressure release valve on the solar loop up near the panel with an outlet pipe running all the way down.

On Saturday we had an impressive demonstration of the energy gathered by our panel. The temperature on the panel went to over 170°C at its height. The pressure release valve was triggered several times - each time with a dramatic noise and a gob of steamy liquid shooting out of the pipe and across our back garden.

One problem with a pressure release valve is that in reducing the pressure in the solar loop it reduces the amount of water in the solar loop and hence making further overheating more likely.

The system has been running normally Monday and yesterday. So I think our plumber was right.

For me it was an interesting experience seeing what sort of mad theories one will adopt when a basic premise is completely wrong.

I was starting with the assumption that when I turned on the mains top-up valve water would go into the system. It was clear that none was getting to the bleeder-valve at the panel ... so rather than contradicting my initial assumption I was adopting a theory about some sort of weird air locks in the solar loop. In fact the failed mains-pressure-reduction valve that the plumber found was letting only a tiny dribble of mains through. So THAT was the source of the problem.

George

[cye]

hi george


if your heat dump was working, i am wondering why the water in your solar loop boiled in the first place. if it boiled because your controller turned off the pump when the water reached X degrees, then you may need to disable that function in your controller , or raise the trigger temp for this in your controller? this way the heat can continue to transfer to the tank, keeping the solar loop from boiling, and letting the heat dump deal with any excess heat?

the temp sensor for the heat dump is normally at the bottom of a solar tank, but as your's has a retrofit coil, i guess it needs to be above the bottom of your solar coil but below the top of the tank.

or maybe your heat dump failed?

[grow]

Cye,
Ah I am with you now.

When we had the problem with the power-supply last autumn the controller may have got re-set to factory-settings. There were some features we set when we first installed it. I have been meaning to go through all the thresholds and settings there may be something mis-set.
George